(a) Field of the Invention
The present invention relates to an oil gallery for a variable valve timing (VVT) apparatus of a cylinder head.
(b) Description of the Related Art
An internal combustion engine generates power by burning a mixture of air and fuel in a combustion chamber. Intake valves are operated by a camshaft in order to intake the air, and the air is drawn into the combustion chamber while the intake valves are open. In addition, exhaust valves are operated by the camshaft, and exhaust gas is expelled from the combustion chamber while the exhaust valves are open.
Optimal opening/closing timing of the intake and exhaust valves depends on the rotation speed of the engine. Continuously variable valve timing (CVVT) apparatus have therefore been developed. These apparatus allow different valve timing depending on the engine speed.
Typically, a CVVT apparatus is operated by hydraulic pressure generated by a hydraulic pump when the engine is running. Engine oil, which is incompressible, is used to provide the hydraulic pressure.
While oil has many merits, the oil is under very harsh conditions while the engine is running, and characteristics, such as viscosity, of the oil may suffer with increasing oil temperature. Also, aeration tends to occur in the oil while the oil circulates around various parts of the engine.
Since air is compressible, the incompressibility of the oil is compromised when aeration occurs. Precision in the operation of the CVVT apparatus is thus also compromised, since the CVVT apparatus is operated by hydraulic pressure of the oil. For example, a delay may occur in an actual operation of the CVVT apparatus with respect to desired timing, and control responsiveness of the CVVT apparatus may suffer. Either of these is detrimental to the performance of the CVVT apparatus.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.